Direction-determination system employing unequal directional patterns



N 5, 9 G. HOFGEN 3,286,261

DIRECTION-DETERMINATION SYSTEM EMPLOYING UNEQUAL DIRECTIONAL PATTERNSFiled June 28. 1963 4 Sheets-Sheet l 7 A BY M: Mm

Nov. 15, 1966 G. HOFGEN 3,286,261

DIRECTION-DETERMINATION SYSTEM EMPLOYING UNEQUAL DIRECTIONAL PATTERNSFiled June 28, 1963 4 Sheets-Sheet 2 o -2 -1 -0,6 -o,a -q100,10,3 0,6 1o FIG. 4

no -z -Q6 230,1001 0,3 96 1 2 w Nov. 15, 1966 a. HDFGEN 3,286,261

DIRECTION-DETERMINATION SYSTEM EMPLOYING UNEQUAL DIRECTIONAL PATTERNSFiled June 28. 1963 4 Sheets-Sheet 5 w -4 .-o,a 1001 as 0,6 4 2 M w z 1as e 2 -2 -21 -1 w United States Patent Office 3,286,261 Patented Nov.15, 1966 3,286,261 DIRECTION-DETERMINATION SYSTEM EMPLOY- ING UNEQUA'LDIRECTIONAL PATTERNS Giinter Hiifgen, Berlin-Lichtenrade, Germany,assignor to International Standard Electric Corporation, New York,

N.Y., a corporation of Delaware Filed June 28, 1963, Ser. No, 291,355Claims priority, application Germany, July 9, 1962, St 19,460 8 Claims.(Cl. 343107) Aircraft landing direction-determination systems(approachbeacons) are known in which the directional patterns servingthe navigation purpose, are lying uniformly and symmetrically inrelation to a center line (landing runway). These patterns may be e.g.directional patterns of either the modulation or frequency deviationtype. These systems, however, require the additional transmission of areference signal. The invention is based on the problem of providing asystem which can be simplified by doing away with this requirement.

The present invention relates to a direction-determination systemoperating on the basis of unequally produced directional patterns, i.e.of such ones which are produced by two spatially separated antennasystems (with the spacing being large with respect to the wavelength)operated at different frequencies. The frequencies are thus that theycan represent both the carrier and a sideband of an amplitude-modulatedoscillation. In particular, the direction-determination system consistsin that one of the two directional patterns is of the amplitudemodulation type, while the other one is of the frequency-deviation type.As regards the mid-vertical line, the two directional patterns arepreferably symmetrical with respect to the connecting line between thetwo antenna systems, but may also be unsymmetrical.

The invention will now be explained in detail with reference to thecopending drawings, in which:

FIG. 1 shows two antenna systems with symmetrical patterns in respect tothe mid-vertical to the line connecting the two arrays;

FIGS. 2 and 3 each show two antenna systems with unequally producedantenna patterns;

FIGS. 4 and 5 are plots of radiation fields of lines having a constantphase difference;

FIG. 6 is a block diagram of a navigation system according to FIG. 2;and

FIG. 7 is a block diagram of a navigation system in accordance with FIG.3.

FIG. 1 shows two antenna systems A and B whose directional patternsextend symmetrically in relation to the mid-vertical to the commonconnecting line. The antenna system A is eg supposed to radiate acarrier oscillation (frequency F which is amplitude-modulated with thesignal frequency f, in such a way that the degree of amplitudemodulation is dependent upon the direction. The directional pattern issupposed to have a figure-ofeight characteristic. To the antenna systemB there is then fed the sideband oscillation (frequency F +AF). Theantenna system B consists of one row comprising a number of singleantennas which are successively fed in a rhythmical succession, so thatin this way, and in the conventional manner, there is simulated anantenna motion of the individual radiators on the linear antenna array.The function of the velocity is supposed to be the same as at themodulation of the carrier oscillation, hence a sine wave function withthe frequency f. The frequency deviation caused on account of theDoppler effect, is direction-dependent. It reaches its maximum in thedirection of the linear antenna array, while being zero vertically inrelation thereto. This directional pattern likewise has afigure-of-eight characteristic.

From the basis of the two unequally produced directional patterns which,however, are of the same characteristic, there may be derived adirection-determination system which is suitable for being received withthe aid of VOR-receivers. This can be realized in that symmetrically inrelation to the center line there is produced a field of lines having aconstant phase difference between the signal obtained from theamplitude-modulated carrier oscillation and the signal obtained from thefrequencym-odulated sideband oscillation, with the phase difference onthe center line itself being zero. To achieve this end a secondmodulation of the same kind of modulation, hence an amplitude modulationin the case of the carrier, and a frequency modulation in the case ofthe sideband, but with a different directional characteristic, is addedto the two direction-dependent modulations in a phaseshifted manner.First of all, consideration will be given to the case (FIG. 2') wherethe additional modulations are undirected, and where the phase shiftbetween the modulated oscillations of the signal frequency amounts toThe local function of the received field intensity produced at the pointP by the antenna system A may then be represented as follows:

The function of time, as well as the pure carrier oscillation which isradiated in an undirected manner, are not represented, because they dono longer appear after having been rectified in the receiver. Thefrequency deviation as produced by the antenna system B at the point P ic r spon in y H =the maximum frequency deviation of thedirectiondependent frequency modulation H =the frequency deviation ofthe additional frequency modulation.

The frequency modulation of the sideband oscillation is containedsubsequently to the rectification in the receiver, in the differenceoscillation (frequency AF) as constituted by the carrier and thesideband, and is con- As a corresponding example there is shOWIl in FIG.4 the field of lines -having a constant phase difference relating to1=2. i

There is now still to be considered the case where the additionalmodulation is likewise direction dependent, The directional patterns aree.g. supposed to have a figure-of-eight characteristic, as shown in FIG.3. When e=E(m -sin w-sin wi+m 'COS w'cos wt) h=H -sin fi-sin wt+H -cosB'cos wt In this case the fields of lines having a constant phasedifference is given by:

As a corresponding example there is shown in FIG. 5 a field of lineshaving a constant phase difference relating to k=2.

The realization of the directional patterns may be effected in the caseof the antenna system A with the aid of crossed dipoles, and in the caseof the antenna system B by providing an elliptical path of the simulatedsideband radiation (arrangement of the single antennas in ellipticalarray).

For carrying out the methods described in conjunction with FIGS. 2 and3, FIG. 6 shows the block diagram relating to a navigation systemaccording to FIG. 2, and FIG. 7 likewise shows a block diagram of anarrangement for carrying out the method according to FIG. 3. In FIG. 6generator 1 is an RF-generator for producing the carrier oscillation,whose angular frequency is S2 =21r-F This oscillation controls twoparallel-arranged output amplifier stages 2 and 3 in the ovenbiasedcondition, so that they are capable of being anode-modulated with a lowdistortion. The two outputs of the output amplifiers are coupled via abridge network 4 consisting of three M4 cables 5 and one 3M4 cable 6, sothat at the output A the sum voltage of both output amplifiers 2 and 3,and at the output A the difference voltage is obtainable.

The control generator 7 produces the low-frequency signal oscillationwhose function of time is cos wt(w=2'rrf :signal angular frequency). Inorder to produce the desired directional patterns at the system A ofFIG. 2 the signal oscillation is subjected to a phase shift by +90 andby 90" with the aid of the phase-shifting devices 8 and 9. Accordingly,the functions of time at the two outputs of the phase shifters are thus+sin wt and sin wt. To the two voltages appearing at the outputs of thephase shifters 8 and 9 there is added with the aid of the adding devices10 and 11 a portion of the signal voltage with the function of time coswt in the necessary ratio which is dependent upon the pattern to beobtained. The sum voltages are amplified in the modulation amplifiers 12and 13. The output voltages of these modulation amplifiers are signifiedas U cos wt+U sin wt and U cos wt -U sin wt; with the aid of thesevoltages there is carried out the amplitude modulation of the twoRF-output amplifiers 2 and 3. Accordingly, the output voltages of theoutput amplifiers may be expressed as follows:

is fed to an unidirectedly radiating antenna (e.g. Alford loop), and thedifference voltage is fed to an antenna 4 having a figure-of-eightpattern (e.g. dipole). way the system A of FIG. 2 is realized.

A second RFagenera'tor 15 produces the sideband oscillation (angularfrequency Sz +AS2=21r[F +AF]), with this oscillation serving to controlthe output amplifier 16. The output of this stage is fed via adistributor 17 to the individual or single antennae B B B of the linearantenna array. The distributor 17 is controlled by the low-frequencyoscillation as produced in the control generator 7; it serves to forwardthe energy as derived from the sideband-output generator 15, in such away to the individual or single antennae B B B that a movement of theradiation center on the linear antenna array is simulated with asinusoidal velocity thereby. An example of such a distributor which canbe used herein is disclosed in the copending patent application of E.Kramar and F. Steiner for Frequency Modulated Approach System filedApril 18, 1961, Serial No. 103,805 now issued as US. Patent No.3,094,697. The function of time of the simulated velocity of theradiation center is sin wt. In this way there is produced the frequencydeviation of the sideband oscillation which, in its magnitude, isdependent upon the direction between the receiving point and the linearantenna array. The necessary additional frequency deviation is obtainedby a frequency modulation of the sideband oscillation produced bygenerator 15, in such a way that a capacitive diode of the servo-system20, having frequency-determining properties with respect to theoscillation produced by generator 15, is subjected to a capacitancemodulation by the signal voltage of the control generator 7.

In order to maintain the frequency spacing between the carrier and thesideband with the necessary accuracy, there is provided a frequencycontroller. In the mixer 21 there is constituted the differencefrequency between the carrier and the sideband. Whenever it deviatesfrom the rated value a control voltage will be produced at the output ofthe controller 22 acting upon the capacitive diode (not shown) of theservo-system 20. In this way the generator 15 is readjusted to the ratedfrequency spacing between the carrier and the sideband.

FIG. 7 shows an RF-generator 30 for producing the carrier voltage(signal) which controls the three parallelarranged output amplifierstages 31, 32 and 33. Since the output voltage s of the output amplifier31 remains unmodulated, the two others (32 and 33) areamplitudemodulated. The function of modulation is that of the controlgenerator 34. The low-frequency signal oscillation of the controlgenerator 34, whose function of time is cos wt, is directly fed to themodulation amplifier 35 via a -phase shifter 36 and to the secondmodulation amplifier 37. The output voltages of the modulationamplifiers are U sin wt and U cos wt; with the aid of these there iscarried out the amplitude modulation of the two RF-output amplifiers 32and 33.

The output voltages of the three output amplifiers may be represented asfollows:

ages between 3 and 5 or B are available at the outputs A and Arespectively. Hence, the voltages are- At the output A d z9 U a sin wteo At the output A d -z9 =U a cos wte o The RF-voltage available at theoutput A is the un- In this modulated carrier voltage (signal) asradiated by an antenna without a directional effect (e.g. Alford loop).The RF-voltages available at the outputSgA1 and A are the pure sidebandvoltages (signals) differing from one another by the modulationamplitude and the modulation phase. They are fed to two antennae havinga figure-ob eight pattern, whose characteristics are shifted by 90spatially with respect to one another (e.g. crossed dipoles), with theradiation centers thereof being in agreement with that of the carrierradiation, and are radiated thereby in a directional fashion. In thisway the system A of FIG. 3 is realized.

The construction of the circuit arrangement for producing the sidebandoscillation (angular frequency Q -i-AQ), including the frequencycontroller, is the same as that shown in FIG. 6. The difference withrespect to the radiation merely resides in the fact that the sidebandradiation must not be moved in a simulated fashion on a linear antennaarray, but on an elliptical path.

While I have described above the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention as set forth in the objects thereof and inthe accompanying claims.

I claim:

1. A direction-determination system operating on the basis of twodirectional patterns which are produced by two spatially separatedantenna systems operated at different frequencies, Whose spacing is aplurality of wavelengths with respect to the transmitted wavelengths,comprising means to produce at one of said antenna systems a pattern ofthe amplitude modulation type, and means to produce at the other antennasystem a pattern of the frequency-deviation type.

2. A direction-determination system according to claim 1 wherein a firstantenna system of said two antenna systems comprises two antennas, meansto produce a first signal which is the sum of two other signals, meansto produce a second signal which is the difference of said two othersignals, means to couple said first signal to said first antenna andmeans to couple said second signal to said second antenna.

3. A direction-determination system according to claim 2 wherein saidfirst antenna is an Alford loop and said second antenna is -a dipole.

4. A direction-determination system according to claim 3 wherein saidsecond antenna system comprises a linear antenna array, means to producea sideband modulation of one of said signals, and means to couplesequentially said sideband signal to the antennas of said linear array.

5. A direction-determination system according to claim 1 wherein a firstantenna system of said two antenna systems comprises three antennas,means to produce a carrier signal, means to produce sideband signals ofsaid carrier and a modulation signal, means to couple said carriersignal to a first of said three antennas and means to couple each saidsideband signals to respective second and third antennas of said threeantennas.

6. A direction-determination system according to claim 5 wherein saidfirst antenna is an Alford loop antenna and each of said second andthird antennas is a dipole antenna.

7. A direction-determination system according to claim 6 wherein thesecond antenna system comprises an antenna array movable on anelliptical path.

8. A direction determination system according to claim 7 furthercomprising means to produce a sideband of said carrier signal and meansto couple sequentially said modulation signal to the antennas of saidantenna array.

References Cited by the Examiner UlSllTED STATES PATENTS 2,543,0812/1951 Watts et al 343 107 x 2,690,558 9/;1954 Harvey 343- 104 2,717,7359/1955 Luck.

3,130,407 4/1964 Kramar 343-407 3,181,159 4/1965 Kramar m1 343106CHESTER L. JUSTUS, Primary Examiner. H. C. WAMSLEY, Assistant Examiner.

1. A DIRECTION-DETERMINATION SYSTEM OPERATING ON THE BASIS OF TWO DIRECTIONAL PATTERNS WHICH ARE PRODUCED BY TWO SPATIALLY SEPARATED ANTENNA SYSTEMS OPERATED AT DIFFERENT FREQUENCIES, WHOSE SPACING IS A PLURALITY OF WAVELENGTHS WITH RESPECT TO THE TRANSMITTED WAVELENGTHS, COMPRISING MEANS TO PRODUCE AT ONE OF SAID ANTENNA SYSTEMS A PATTERN OF THE AMPLITUDE MODULATION TYPE, AND MEANS TO PRODUCE AT THE OTHER ANTENNA SYSTEM A PATTERN OF THE FREQUENCY-DEVIATION TYPE. 